Integrated pressure sensor with double measuring scale, pressure measuring device including the integrated pressure sensor, braking system, and method of measuring a pressure using the integrated pressure sensor

ABSTRACT

A pressure sensor with double measuring scale includes: a flexible body designed to undergo deflection as a function of a the pressure; piezoresistive transducers for detecting the deflection; a first focusing region designed to concentrate, during a first operating condition, a first value of the pressure in a first portion of the flexible body so as to generate a deflection of the first portion of the flexible body; and a second focusing region designed to concentrate, during a second operating condition, a second value of said pressure in a second portion of the flexible body so as to generate a deflection of the second portion of the flexible body. The piezoresistive transducers correlate the deflection of the first portion of the flexible body to the first pressure value and the deflection of the second portion of the flexible body to the second pressure value.

BACKGROUND Technical Field

The present disclosure relates to an integrated pressure sensor withdouble measuring scale, to a pressure measuring device including theintegrated pressure sensor, to a braking system, and to a method ofmeasuring a pressure that uses the integrated pressure sensor. Inparticular, the ensuing treatment will make explicit reference, withoutthis implying any loss of generality, to use of said pressure sensor ina braking system of a vehicle, in particular an electromechanicalbraking system of the BbW (Brake-by-Wire) type.

Description of the Related Art

As is known, disk-brake systems of a traditional type for vehiclescomprise a disk fixed with respect to a respective wheel of the vehicle,a calliper associated with the disk, and a hydraulic control circuit.The calliper houses within it pads of friction material, and one or morepistons connected to the hydraulic control circuit. Following upon anaction, exerted by a user of the vehicle, on the brake pedal, a pump inthe hydraulic control circuit pressurizes a fluid contained in thecircuit itself. Consequently, the pistons, equipped with purposelyprovided sealing elements, come out of respective seats and come topress the pads against the surface of the disk, in this way exerting abraking action on the wheel.

Recently, so-called DbW (Drive-by-Wire) systems have been proposed,which envisage electronic control of the main functions of a vehicle,for example the steering system, the clutch, and the braking system. Inparticular, electronically controlled braking systems have beenproposed, which envisage replacement of the hydraulic calipers withactuators of an electromechanical type. In detail, appropriate sensorsdetect operation of the brake pedal and generate correspondingelectrical signals, which are received and interpreted by an electroniccontrol unit. The electronic control unit then controls intervention ofthe electromechanical actuators (for example, pistons driven by anelectric motor), which exert the braking action on the correspondingbrake disks, through the pads. The electronic control unit furtherreceives from sensors associated to the braking system information onthe braking action exerted by the electromechanical actuators so as toprovide an appropriate closed-loop feedback control, for example, via aPID (Proportional-Integral-Derivative) controller. In particular, theelectronic control unit receives information on the pressure exerted byeach actuator on the respective brake disk.

To measure the aforesaid pressure, pressure sensors are used with highsensitivity both at low pressures and at high pressures, and likewisewith a high full-scale value. In fact, there is particularly felt theneed to measure pressure with a double measuring scale in order tomeasure both low pressures and high pressures with high precision.Furthermore, the force with which the pads are pressed against the diskmay assume values from 0 N up to a maximum comprised in the range 10,000to 35,000 N, according to the braking system.

There are currently known sensors capable of measuring high pressurevalues, which are made with a steel core, fixed on which arestrain-gauge elements.

The strain-gauge elements detect the geometrical deformation of the coreto which they are associated by variations of electrical resistance.However, these sensors, for reasons of reliability, size, and costs maybe applied and used only for characterization and development of abraking system of the type described previously, but not in theproduction stage. Furthermore, they do not have a high precision andhave only one measuring scale.

Likewise known are integrated pressure sensors, obtained withsemiconductor technology. These sensors typically comprise a thinmembrane suspended over a cavity made in a silicon body. Diffused withinthe membrane are piezoresistive elements connected together to form aWheatstone bridge. When subjected to a pressure, the membrane undergoesdeformation, causing a variation of resistance of the piezoresistiveelements, and thus an unbalancing of the Wheatstone bridge. However,such sensors may not be used for measurement of high pressures, in sofar as they have low full-scale values (namely, in the region of 10kg/cm²), in particular considerably lower than the pressure values thatare generated in the braking systems described previously.

A solution to the aforementioned problems is disclosed by U.S. Pat. No.7,578,196, where, for measurement of high pressures, a membrane sensoris proposed provided with first piezoresistive elements, set in theproximity of the membrane, and second piezoresistive elements, set at adistance from the membrane, in a bulk area that is solid and compact.The first piezoresistive elements are designed to detect a deflection ofthe membrane that undergoes deformation under the action of lowpressures, until a maximum deflection (saturation) is reached. Thesecond piezoresistive elements are designed to detect a stress of atransverse type (but not longitudinal, in so far as there is no bendingor phenomena of curving of the bulk area) that acts on the secondpiezoresistive elements as a result of an increase in pressure beyondthe saturation pressure of the membrane.

This type of sensor provides a good accuracy of measurement at lowpressures (signal supplied by the first piezoresistive elements), but apoor accuracy at high pressures (signal supplied by the secondpiezoresistive elements). Furthermore, this type of sensor does notdiscriminate between pressure variations lower than a minimum detectionthreshold.

For the feedback-control system of the braking system to functionoptimally, it is expedient also for the measurements made at highpressures to be accurate and sensitive to minimal pressure variations.

BRIEF SUMMARY

Some embodiments of the present disclosure are a pressure sensor, apressure measuring device, including the integrated pressure sensor, anda method of measuring a pressure that uses the pressure sensor whichwill enable the aforementioned disadvantages and problems to be overcomeand in particular will present a double measuring scale, a highfull-scale value, and high accuracy and sensitivity, so as to measureboth high pressures and low pressures with a good level of precision.

According to the present disclosure, an integrated pressure sensor withdouble measuring scale, a pressure measuring device including theintegrated pressure sensor, a braking system, and a method of measuringa pressure that uses the integrated pressure sensor are consequentlyprovided as defined in the annexed claims.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

For a better understanding of the present disclosure, preferredembodiments thereof are now described, purely by way of non-limitingexample and with reference to the attached drawings, wherein:

FIG. 1 illustrates a block diagram of a braking system of abrake-by-wire electromechanical type;

FIG. 2 is a cross-sectional view (not in scale) of a pressure sensorobtained according to one embodiment of the present disclosure;

FIG. 3 shows a Wheatstone-bridge circuit formed by piezoresistiveelements, integrated in the pressure sensor of FIG. 2;

FIG. 4 is a perspective view of the pressure sensor of FIG. 2;

FIG. 5 is a cross-sectional view (not in scale) of a pressure sensorobtained according to a further embodiment of the present disclosure;

FIG. 6 is a cross-sectional view (not in scale) of a pressure sensorobtained according to a further embodiment of the present disclosure;

FIG. 7 shows an electrical signal generated at output from the pressuresensor of FIG. 6 as a function of a pressure to which the sensor itselfis subjected in use; and

FIGS. 8-12 show respective embodiments of pressure sensors designed totransfer electrical signals, generated as a function of a pressure towhich the sensor is subject in use, at output from the pressure sensor.

DETAILED DESCRIPTION

FIG. 1 shows an example of block diagram of a braking system 1 of anelectromechanical type (a so-called “brake-by-wire” system), comprising:a brake pedal 2; first sensors 3 designed to detect the travel C andspeed of actuation v of the brake pedal 2; an electronic control unit 4,connected to the first sensors 3; an electromechanical actuator 5connected to the electronic control unit 4, and constituted by anelectric motor 6 and by a piston 7, which is connected to the electricmotor 6 for example by a connection element of the wormscrew type (notillustrated); a brake disk 8, connected to the electromechanicalactuator 5 and fixed with respect to a wheel of a vehicle (in a wayknown and not illustrated); and second sensors 9, which are designed todetect information regarding the braking action exerted by theelectromechanical actuator 5 on the brake disk 8 and arefeedback-connected to the electronic control unit 4.

In use, the first sensors 3 send data regarding the travel C and speedof actuation v of the brake pedal 2 to the electronic control unit 4,which, as a function of said data, generates a control signal (involtage V or current I) for the electromechanical actuator 5 (inparticular, for the electric motor 6). As a function of said controlsignal, the electric motor 6 generates a torque that is converted into alinear movement of the piston 7 by the connection element of thewormscrew type. Consequently, the piston 7 presses on the brake disk 8(via pads of abrasive material, not illustrated) so as to brake rotationthereof. The second sensors 9 detect the value of the pressure P exertedby the piston 7 on the brake disk 8 and the position x of the piston 7with respect to the brake disk 8, and send said feedback data to theelectronic control unit 4. The electronic control unit 4 thus implementsa closed-loop control (for example, a PID control) of the brakingaction.

According to one aspect of the present disclosure, the second sensors 9comprise a pressure sensor according to any one of the embodimentsdescribed in what follows, in particular of an integrated type, whichare obtained in MEMS technology and are designed to measure the pressureP exerted by the piston 7 on the brake disk 8. In a way not illustrated,the pressure sensor 15 is housed in a casing of the electromechanicalactuator 5 and is configured in such a way as to be sensitive to thepressure P exerted by the piston 7.

In detail, as represented in FIG. 2 in a reference system of orthogonalaxes X, Y, Z, the pressure sensor 15 comprises a monolithic body 16 ofsemiconductor material, preferably silicon, in particularmonocrystalline silicon, for example of an N type with orientation (100)of the crystallographic plane. The monolithic body 16 has a quadrangularcross-section, for example square of side 1 (measured along the axis Xor Y) comprised, for example, between 1 mm and 20 mm, preferably between10 mm and 15 mm, delimited at the top by a first surface 16 a and at thebottom by a second surface 16 b, which is opposite and parallel to thefirst surface 16 a. The monolithic body 16 has a thickness, measuredalong Z between the first and second surfaces 16 a, 16 b, equal to w andsubstantially uniform, for example comprised between 50 and 900 μm,preferably comprised between 500 and 900 μm, in particular equal to 720μm.

The monolithic body 16 comprises a bulk region 17 and a first cavity 18,buried in the monolithic body 16. The first cavity 18 has across-section that is, for example, square with side comprised between300 and 400 μm and a thickness (measured along the axis Z) comprisedbetween 2 and 6 μm, for example 4 μm. The first cavity 18 is separatedfrom the first surface 16 a by a thin portion of the monolithic body 16,which forms a membrane 19, which has a thickness comprised, for example,between 1 and 60 μm, preferably between 4 and 10 μm. The bulk region 17is thus the portion of the monolithic body 16 that surrounds themembrane 19 and the first cavity 18.

The membrane 19 is flexible and is able to undergo deflection in thepresence of external loads. In particular, as described in detailhereinafter, the membrane 19 undergoes deformation as a function of aforce or pressure P acting on the monolithic body 16. According to oneembodiment, the thickness of the membrane 19 is smaller than thethickness of the first cavity 18 in order to prevent shear stresses inthe points of constraint of the membrane 19, which might cause failureof the membrane itself.

The first cavity 18 may be obtained with the manufacturing processdescribed in the U.S. Patent No. 8,173,513, which is incorporated byreference herein in its entirety.

Present at least partially within the membrane 19 are firstpiezoresistive sensing elements 28 (in particular, four in number, setat the vertices of an ideal cross centered at the center of the membrane19), constituted by regions with a doping, for example, of a P type. Thefirst piezoresistive sensing elements 28 may be obtained via diffusionof dopant atoms through an appropriate diffusion mask, and have, forexample, an approximately rectangular cross-section. In addition, thefirst piezoresistive sensing elements 28 may be connected together so asto form a Wheatstone-bridge circuit.

Alternatively, the first piezoresistive sensing elements 28 may formpart of a ring oscillator circuit.

In a surface portion of the bulk region 17, in a position separate anddistinct from the membrane 19, second piezoresistive sensing elements 29are present (in particular, four in number, set at the vertices of afurther ideal cross centered at the center of the membrane 19), whichare also, for instance, formed by regions having, for example, a dopingof a P type obtained by diffusion. The second piezoresistive sensingelements 29 are separated from the membrane 19 (and thus from the firstpiezoresistive sensing elements 28) by a distance (measured along theaxis X) equal to or greater than, for example, 10 μm, preferably 50 μm,so as not to be affected significantly by the stresses on the membrane19 (and on the first piezoresistive sensing elements 28) when the forceP acts. In particular, the second piezoresistive sensing elements 29 areintegrated in a solid and compact portion of the bulk region 17, havinga thickness substantially equal to the distance w.

According to one embodiment, an interface layer 34 coats the firstsurface 16 a of the monolithic body 16. The interface layer 34 may be amono-layer or a multi-layer comprising an elastic material, such as forexample polyamide, or else may be a mono-layer or a multi-layer ofdielectric material, for example silicon oxide, or alternatively amulti-layer comprising a silicon-oxide layer on which a polyamide layerextends. The interface layer 34 may comprise one or more metallizationlevels (not illustrated), interconnected by connection vias.

A first substrate 32, for example of semiconductor material, such assilicon, extends over the interface layer 34, coupled to the interfacelayer 34 by anchorage elements 31 that extend between the interfacelayer 34 and the first substrate 32, in peripheral regions of theinterface layer 34 and of the underlying monolithic body 16. Consideredherein as peripheral regions are those regions of the monolithic body 16that extend (when considered in the planes XY, XZ and YZ) outside thesecond sensing elements 29. In particular, the anchorage elements 31extend along the entire perimeter of the interface layer 34 and of themonolithic body 16, outside the second piezoresistive sensing elements29. The anchorage elements 31 laterally surround and define a cavity 36that extends between the first substrate 32 and the interface layer 34.

The anchorage elements 31 are made, for example, of dielectric material,such as silicon oxide or silicon nitride, and are obtained withdeposition and etching steps, in themselves known.

A first focusing region 30, which is also for example of dielectricmaterial, such as silicon oxide or silicon nitride, extends between, andin direct contact with, the interface layer 34 and the first substrate32. In particular, the first focusing region 30 extends over themembrane 19, i.e., at least partially aligned to the membrane 19 alongthe axis Z. In this way, in use, the first focusing region 30 focusesthe pressure P on the membrane 19 itself, forcing it to undergodeformation. The first focusing region 30 is obtained during the samesteps of production of the anchorage elements 31.

The pressure sensor 15 further comprises a second substrate 35, made,for example, of semiconductor material, such as silicon (having athickness comprised, for instance, between 50 and 900 μm, preferablybetween 500 and 900 μm, in particular 720 μm), or ceramic material, orglass, or some other material still, having a similar coefficient ofelasticity, which extends facing the second surface 16 b of themonolithic body 16, mechanically coupled to the second surface 16 b byanchorage elements 37 that extend between the second surface 16 b of themonolithic body 16 and a respective surface 35 a of the second substrate35, at least in part in peripheral regions of the second surface 16 b ofthe monolithic body 16. As defined previously, considered as peripheralregions are those regions of the monolithic body that extend, as viewedin the planes XY, XZ, and YZ, outside the second piezoresistive sensingelements 29. However, in this case, as is on the other hand illustratedin FIG. 2, the anchorage elements 37 extend in part, once again asviewed in the plane XY, on top of the second piezoresistive sensingelements 29.

In particular, the anchorage elements 37 extend along the entireperimeter of the second surface 16 b of the monolithic body 16 and ofthe surface 35 a of the second substrate 35 so as to define a secondcavity 38 between the second surface 16 b and the surface 35 a.

The anchorage elements 37 are of dielectric material, for examplesilicon oxide or silicon nitride, and have a thickness, along Z,comprised for example between 0.1 μm and 20 μm, for example 1 μm. Thedistance (along Z) between the second surface 16 b and the surface 35 adefines the height of the second cavity 38, substantially equal to thethickness of the anchorage elements 37.

Extending further between the interface layer 34 and the first substrate32 and in the cavity 36 are one or more second focusing regions 33,which are coupled to the first substrate 32 (but not to the interfacelayer 34) and have a thickness, along Z, smaller than the thickness,once again along Z, of the first focusing region 30. In particular, thesecond focusing regions 33 have a thickness such that, when the membrane19 comes into contact with the bottom of the first cavity 18, orsaturates (i.e., it is completely deflected, thus closing the firstcavity 18), or reaches the desired full-scale value, the second focusingregions 33 are in direct contact with the interface layer 34. In otherwords, the distance (along Z) between the second focusing regions 33 andthe interface layer 34 is equal to or smaller than the thickness (alongZ) of the first cavity 18.

As an alternative to what has been described, the second focusingregions 33 may be coupled to the interface layer 34 but not to the firstsubstrate 32, with which they come into direct contact when the membrane19 reaches the bottom of the cavity 18, or saturates, or reaches thedesired full-scale value.

According to a further embodiment, the second focusing regions 33 may beprovided coupled in part to the interface layer 34 and in part to thefirst substrate 32.

Thus, when a pressure P is applied in use on the pressure sensor, themembrane 19 undergoes deflection until it comes into contact with thebottom of the cavity 18. A minimum pressure value P_(MAX1) for bringingthe membrane 19 into contact with the bottom of the cavity 18 dependsupon the thickness of the membrane 19 and upon the material of which itis made. For instance, the membrane 19 is produced in such a way as tocome into contact with the bottom of the cavity 18 when it is subjectedat least to a pressure P_(MAX1) comprised between 8 and 50 N. Inparticular, with a membrane 19 of monocrystalline silicon having athickness, along Z, equal to 8 μm, the pressure value P_(MAX1) is 10 N.

Intermediate pressure values P_(INT1)<P_(MAX1) are such as to causeprogressive deflection of the membrane 19 (the higher the current valueof R_(INT1), the greater the deflection of the membrane), but not suchas to bring it into contact with the bottom of the cavity 18.

As the pressure P increases, the second focusing regions 33, togetherwith the first focusing region 30, co-operate to bring about deflectionof the monolithic body 16, which thus behaves, as a whole, as a secondmembrane suspended over the second cavity 38. A minimum pressure valueP_(MAX2) such as to bring the monolithic body 16 into contact with thebottom 35 a of the cavity 38 depends upon the thickness of themonolithic body 16 and upon the material of which it is made. Forinstance, the monolithic body 16 is produced in such a way as to comeinto contact with the bottom 35 a of the cavity 38 when it undergoes apressure at least equal to P_(MAX2) higher than P_(MAX1) (and having amaximum value such as not to damage the pressure sensor, for example afull-scale value comprised between 10 and 20 kN). In a particularexample, with a monolithic body 16 of monocrystalline silicon having athickness w of 720 μm, the pressure value P_(MAX2) is 10 kN.

Intermediate pressure values P_(INT2) such thatP_(MAX1)<P_(INT2)<P_(MAX2) are such as to cause progressive deflectionof the monolithic body 16 (the higher the current value of P_(INT2), thegreater the deflection of the monolithic body 16), but not to bring themonolithic body 16 into contact with the bottom 35 a of the cavity 38.

The second piezoresistive sensing elements 29 have the function, in use,of detecting the degree of deflection of the second membrane, i.e., ofthe monolithic body 16, when the deflection of the first membrane 19 ismaximum (saturation condition). For this reason, it is preferable toform the second piezoresistive sensing elements 29 sufficiently far fromthe first membrane 19 so that they will not be affected by itsdeflection, but in any case in a region of the monolithic body 16 thatundergoes deflection when the first membrane 19 is saturated. Forinstance, they may be set substantially aligned, along Z, withrespective peripheral regions of the second cavity 38, i.e., regions ofthe second cavity 38 close to or bordering on the anchorage elements 37.

As has been anticipated, the general operation of the pressure sensor 15is based upon the so-called piezoresistive effect, whereby a stressapplied on a piezoresistive element causes a variation of resistancethereof. In the case of semiconductor materials, such as silicon, thestress applied, in addition to determining a variation of the dimensionsof the piezoresistive element, brings about a deformation of thecrystalline lattice and thus an alteration of the mobility of themajority charge carriers and a variation of resistivity. For instance,in silicon, to a deformation of 1% of the crystalline lattice, therecorresponds a variation of approximately 30% of the mobility of themajority charge carriers. In particular, the variation of resistance iscaused by stresses acting both in a parallel direction (so-calledlongitudinal stresses) and in a direction normal to the plane in whichthe piezoresistive elements lie (so-called transverse stresses). Thevariation of resistance of a piezoresistive element may in general beexpressed by the following relation:

$\frac{\Delta\; R}{R} = {\frac{\pi_{44}}{2}\left( {\sigma_{l} - \sigma_{t}} \right)}$where R is the resistance of the piezoresistive element, ΔR is thevariation of said resistance, Π₄₄ is one of the piezoresistivecoefficients of the semiconductor material, for example equal to138.1·10⁻¹¹ Pa⁻¹ for monocrystalline silicon of a P type, and σ₁, σ₂are, respectively, the longitudinal stress and the transverse stress towhich the piezoresistive element is subjected.

With reference to the pressure sensor 15 of FIG. 2, the monolithic body16 is arranged in such a way that the pressure P to be measured causes astress in a direction normal to the first main outer surface 16 a (i.e.,in this embodiment, along Z).

In particular, in a first operating condition, the pressure P bringsabout a deformation of the membrane 19, which is forced to undergodeformation. This deformation induces longitudinal and transversemechanical stresses in the first piezoresistive sensing elements 28,which consequently modify the value of resistance. Considering, forexample, a Wheatstone-bridge configuration of the first piezoresistivesensing elements 28, generally they are set in such a way that part ofthem (e.g., two of them) undergo a compressive stress, and the remainingones (the other two, in the case provided by way of example of fourpiezoresistors) undergo tensile stress so as to increase the sensitivityof the corresponding Wheatstone-bridge circuit. The variation ofresistance of the first piezoresistive sensing elements 28 thus causesan unbalancing of the Wheatstone-bridge circuit, which generates avoltage signal at output from the Wheatstone-bridge circuit, which maybe detected by an appropriate read circuit.

In addition, in a second operating condition in which the pressure Passumes a value higher than the one required for bringing the secondfocusing regions 33 into contact with the interface layer 34, adeformation of the monolithic body 16 is induced that brings about alongitudinal and transverse mechanical stress in the secondpiezoresistive sensing elements 29, which consequently modify the valueof resistance, as described with reference to the first piezoresistivesensing elements 28.

In detail, one aspect of the present disclosure is based upon therealization that for low values of the pressure P, the deformation ofthe second piezoresistive sensing elements 29 is practically negligible.Instead, the membrane 19 is induced to undergo deformation, causing acorresponding deformation of the first piezoresistive sensing elements28, which is detected by the read circuit in order to supply ameasurement of the pressure P applied. As the pressure P increases, thedeformation of the membrane 19 increases until the membrane 19 itselfcomes into contact with the bottom of the underlying first cavity 18,thus saturating the pressure value supplied at output (in so far as anyfurther deformation is not possible). In particular, this saturation mayoccur for values of the pressure P for example around 10 N.

At this point, a further increase in the pressure P begins to affect theentire first main outer surface 16 a and to cause a deflection of themonolithic body 16, causing a consequent non-negligible variation of theresistance of the second piezoresistive sensing elements 29, from whichthe value of the pressure P is derived. Saturation of the secondmembrane obtained by the monolithic body 16 occurs for values of thepressure P around 10 kN.

Consequently, the measurements of pressure supplied by the first andsecond piezoresistive sensing elements 28, 29 are independent andcomplementary, given that said elements intervene for different valuesof the pressure P. The pressure sensor 15 thus has a first measuringscale, valid for low values of the pressure P and a full-scale valuearound 10 N (determined by the action of the membrane 19 and of thefirst piezoresistive sensing elements 28, which thus form together anelement sensitive to low pressures), and a second measuring scale, validfor high values of the pressure P and having a full-scale value around10 kN (determined by the action of the monolithic body 16 and of thesecond piezoresistive sensing elements 29, which thus form together anelement sensitive to high pressures). The first measuring scale is moreprecise than the second, given that the membrane 19 is sensitive to evenminimal variations of the pressure P.

The pressure sensor 15 presents a considerable strength in regard tohigh pressures. As is known, in fact, monocrystalline silicon has a highultimate strength in regard to compressive stresses, in particular up to2 GPa, according to the crystallographic orientation, so that it is ableto withstand, with ample margin, the maximum pressure values that arisewithin a braking system. Furthermore, the deflections of the membrane 19in a vertical direction are limited by the relatively small thickness ofthe first cavity 18, thus preventing failure of the membrane 19 for highpressure values.

The first piezoresistive sensing elements 28 may, for example, beconnected together to form a Wheatstone-bridge circuit (FIG. 3), withresistors that vary in the same direction set on opposite sides of thebridge so as to increase the sensitivity of the circuit. TheWheatstone-bridge circuit is supplied with a supply voltage V_(in1) andsupplies an output voltage V_(out1).

The second piezoresistive sensing elements 29 may in turn be connectedso as to form, for example, an own Wheatstone-bridge circuit, similar tothe one illustrated in FIG. 3. Advantageously, the particulararrangement of the piezoresistors in the Wheatstone-bridge circuitenables a differential measurement to be made, where the variations ofresistance due to the environmental parameters (for example,temperature) cancel out, thus rendering the second output voltageV_(out1), and thus the value of the pressure P measured, insensitive tosaid parameters.

Note, in particular, that the first and second piezoresistive sensingelements 28, 29 are not electrically connected together and form part oftwo distinct and independent electronic read circuits (so as to provide,as highlighted previously, the two measuring scales of the pressuresensor 15). In particular, for low values of the pressure P, the voltageat output from the circuit formed by the second piezoresistive elements29 is substantially zero, whereas the voltage V_(out1) at output fromthe circuit formed by the first piezoresistive elements 28 is used by anappropriate electronic measuring circuit (of a per se known type andcomprising, for example, at least one instrumentation amplifier) formeasuring the pressure P. Instead, for high values of the pressure P,the output voltage V_(out1) of the circuit formed by the firstpiezoresistive elements 28 saturates, and the electronic measuringcircuit obtains the measurement of the pressure P from the outputvoltage V_(out2) of the circuit formed by the second piezoresistiveelements 29.

FIG. 4 shows a perspective view of a portion 15′ of the pressure sensor15 of FIG. 2. In particular, the portion 15′ represented in FIG. 4 is aportion of pressure sensor 15 cut along the plane of section of FIG. 2.Joining of two specular portions 15′ forms the pressure sensor 15.

As may be seen from FIG. 4, the anchorage elements 31 extend along theentire perimeter of the monolithic body 16, forming a frame on which thefirst substrate 32 rests. Likewise, the second focusing regions 33extend within the region defined by the anchorage elements 31,mechanically isolated from the latter region so as to be able to undergodeflection together with the first substrate 32.

In addition, the second focusing regions 33 have a recess within whichthe first focusing region 30 is housed. The second focusing regions 33are thus also separate from the first focusing region 30 so as not tohave constraints in order to undergo deflection together with the firstsubstrate 32. In the embodiment of FIG. 4, the second focusing regions33 extend joined to one another to form a single region. However,according to different embodiments, they may be mechanicallyseparate/isolated from one another, for example isolated from oneanother at the recess that houses the first focusing region 30.

The anchorage elements 37 have a shape and extension similar to that ofthe anchorage elements 31, and define the second cavity 38, inside theframe formed by the anchorage elements 37.

According to a further embodiment (not illustrated in the figure), theanchorage elements 31 and the second focusing regions 33 are joinedtogether, but with a respective thickness (along Z) that varies alongthe axis X so that the anchorage elements 31 and the second focusingregions 33 have a different thickness, as already described.

FIG. 5 is a lateral sectional view of a further embodiment of a pressuresensor 50, according to a further aspect of the present disclosure.

The pressure sensor 50 comprises a base substrate 52, for example ofsemiconductor material such as silicon, or ceramic material, or glass,or some other material still, having a similar coefficient ofelasticity, mechanically coupled to a monolithic body 56 ofsemiconductor material, such as silicon, by one or more anchorageelements 54. The anchorage elements 54 are similar to the anchorageelements 31 of FIGS. 2 and 4, and are not described any further herein.

The monolithic body 56 is similar to the monolithic body 16 describedpreviously, and houses a buried cavity 58. The buried cavity 58corresponds to the first cavity 18 of FIG. 2 and is obtained with thesame manufacturing method. Extending between the buried cavity 58 and asurface 56 a of the monolithic body 56 is a flexible membrane 59 that isable to undergo deflection in the presence of external loads. Inparticular, as already described in detail with reference to themembrane 19 of FIG. 2, the membrane 59 undergoes deformation as afunction of the pressure P acting on the monolithic body 56.

Present at least partially within the membrane 59 are firstpiezoresistive sensing elements 68, which are similar to thepiezoresistive elements 28 of FIG. 2 and have the same purpose. Inparticular, the first piezoresistive sensing elements 68 are four innumber, are constituted by regions with a doping of a P type, and areconnected together so as to form a Wheatstone-bridge circuit. In a perse known manner, the resistance of the first piezoresistive sensingelements 68 is variable as a function of the deformation of the membrane59.

In a position separated and distinct from the membrane 59, secondpiezoresistive sensing elements 69 are present, which are similar to thepiezoresistive elements 29 of FIG. 2 and have the same purpose. Theseare also constituted by regions with a doping of a P type and areseparated from the membrane 59 by a distance such as not to be affectedsignificantly by the stresses acting on the membrane 59 during a firstoperating condition of action of the force P (e.g., up to 10 N).Hereinafter, the force P will refer indifferently to a force or apressure that the same force exerts on a surface.

A first focusing region 66, similar to the first focusing region 30 ofFIGS. 2 and 4, extends between the substrate 52 and the monolithic body56, in an area corresponding to the membrane 59.

Second focusing regions 73, similar to the second focusing regions 33 ofFIG. 2, extend between the first focusing region 66 and the anchorageelements 54. The second focusing regions 73 have a thickness, along Z,smaller than the thickness, along Z, of the anchorage elements 54 and ofthe first focusing region 66. Advantageously, the second focusingregions 73 are already aligned to the first and second piezoresistivesensing elements 68, 69. Note that here, as likewise in the ensuingfigures, for simplicity of representation the interface layer 34 hasbeen omitted.

In use, when the pressure P is applied, the presence of the firstfocusing region 66 causes a deflection of the membrane 59, whichundergoes deflection in proportion to the pressure applied, until itcomes into contact with the internal wall of the cavity 58 (firstoperating condition); as the pressure P increases, the monolithic body56 undergoes deflection in the area corresponding to the portionsthereof that house the second focusing regions 73 (i.e., in the areacorresponding to the portions of the monolithic body 56 that extendbetween the anchorage elements 54 and the first focusing region 66),until the second focusing regions 73 come into contact with thesubstrate 52, thus determining a full-scale value for the measurement ofthe deflection, and preventing undesirable failure of or damage to themonolithic body 56 (second operating condition). The monolithic body 56thus behaves as a second membrane suspended on the cavity presentbetween the monolithic body 56 itself and the substrate 52.

FIG. 6 shows a further embodiment of a pressure sensor 80 according tothe present disclosure.

The pressure sensor 80 comprises a monolithic body 82, for example ofsemiconductor material (e.g., silicon). The monolithic body 82 extendsbetween a first substrate 88 and a second substrate 84. In greaterdetail, the monolithic body 82 is mechanically coupled to the secondsubstrate 84 by anchorage elements 85 similar to the anchorage elements37 described with reference to FIG. 1. Thus, the anchorage elements 85extend along a peripheral, or perimetral, region of the monolithic body82 and define a cavity 86. According to one embodiment, the anchorageelements 85 surround the cavity 86 completely so that said cavity 86 iscompletely isolated from outside. According to a different embodiment,the cavity 86 is only partially surrounded by the anchorage elements 85.Set on the side of the monolithic body 82 opposite to the side on whichthe anchorage elements 85 extend is the first substrate 88, for exampleof semiconductor material, similar to the first substrate 32 describedwith reference to FIG. 2, or ceramic material, or glass, or some othermaterial still, having a similar coefficient of elasticity. Inparticular, the first substrate 88 is mechanically coupled to themonolithic body 82 by anchorage elements 91 similar to the anchorageelements 31 of FIG. 2. Furthermore, extending between the firstsubstrate 88 and the monolithic body 82 are first and second focusingregions 90, 93 similar to the respective first and second focusingregions 30, 31 of FIG. 2, and thus not described any further. In avariant (not illustrated), the second focusing regions 93 may bearranged on the monolithic body 82, like the second focusing regions 73of FIG. 5.

Piezoresistive sensing elements 94 (in particular four in number,electrically connected together to form a Wheatstone-bridge circuit),constituted by regions with a doping of a P type, extend in themonolithic body 82 in the proximity of the surface thereof facing thefirst substrate 88. More in particular, the piezoresistive elementsextend in a portion of the monolithic body 82 between the anchorageelements 91 and the second focusing regions 93, specularly with respectto the first focusing region 90.

In use, during a first operating condition, a pressure, or force, P isapplied to the first substrate 88 and is transferred, by the anchorageelements 91 and of the first focusing region 90, to the monolithic body82. The monolithic body 82 consequently undergoes deflection, generatinga longitudinal and transverse stress in the area corresponding to thepiezoresistive sensing elements 94. FIG. 7 shows, qualitatively, theplot of the output voltage signal generated by the Wheatstone-bridgecircuit during the first operating condition (V_(out1)) and during thesecond operating condition (V_(out2)).

If the force P applied is such as to bring the second focusing regions93 to come into contact with the monolithic body 82 (in the example ofFIG. 7, this event there corresponds to a pressure of 10 N and generatesat output from the bridge circuit a voltage V_(MAX1)), the pressuresensor 80 enters a second operating condition, where the monolithic body82 continues to undergo significant deflection in the area correspondingto the regions comprised between the anchorage elements 91 and thesecond focusing regions 93, i.e., in the portion thereof that houses thepiezoresistors 94. In the example of FIG. 7, at the pressure of 10 kNthe second focusing regions 93 come into contact with the monolithicbody 82, and an output voltage V_(out2) is generated by the bridgecircuit equal to V_(MAX2)>V_(MAX1).

As may be noted from FIG. 7, in the second operating condition, thevoltage V_(out2) at output from the Wheatstone-bridge circuit changesslope with respect to the voltage V_(out1). Knowing the plot of thesignal V_(out) at output from the bridge circuit (which may be obtainedexperimentally in a per se known manner by applying an increasing forceP and measuring the output V_(out)) it is thus possible to identify, ateach instant of operation of the pressure sensor 80, in which operatingcondition it is by correlating the output voltage value V_(out) with theeffective pressure value P to which the pressure sensor is subjected.

FIG. 8 is a cross-sectional view of the pressure sensor 15 of FIG. 2 inwhich the second substrate 35 has an extension, in the plane XY, greaterthan the respective extension of the monolithic body 16. In turn, themonolithic body 16 has an extension, in the plane XY, greater than therespective extension of the first substrate 32. In this way, it ispossible to provide electrical-contact pads 98 suitably connected (in away known and not illustrated herein), for example to the first andsecond piezoresistive sensing elements 28, 29 on the top surface 16 a ofthe monolithic body 16 alongside the first substrate 32. By way ofexample, only two pads 98 are visible in FIG. 8, but they may be any innumber, as required. Between the pads 98 and the first and secondpiezoresistive sensing elements 28, 29 a further circuit may be present,for example an interface circuit, or an acquisition circuit, or aconversion circuit so as to encode appropriately the value of thephysical quantity measured by the pressure sensor 15. It is likewisepossible to provide respective electrical-contact pads 99 (electricallycoupled to conductive paths, not illustrated) on the top surface 35 a ofthe second substrate 35. By way of example, only two pads 99 are visiblein FIG. 8, but they may be any in number, as desired.

The pads 98 are electrically connected to respective electrical outputterminals of the Wheatstone-bridge circuits formed, respectively, by thefirst piezoresistive sensing elements 28 and by the secondpiezoresistive sensing elements 29. The electrical connection betweenthe pads 98 and the pads 99 is obtained by wire bonding 97. With the useof appropriate conductive paths coupled to the pads 99 it is thuspossible to transfer the electrical signal supplied by theWheatstone-bridge circuits outside the pressure device 15, for exampleto the control unit 4 of FIG. 1. Further electrical contact pads (notillustrated) may be provided for sending the power supply to thepressure sensor.

FIG. 9 shows a further embodiment of a pressure sensor 101, where theelectrical signal generated by the first and second piezoresistivesensing elements 28, 29 is transferred outside the pressure sensor 101by inductive coupling.

In this embodiment, one or more inductors 102 are integrated in theinterface layer 34 (or, alternatively, in the monolithic body 16 on thesurface 16 a), and respective one or more inductors 104 are integratedin the first substrate 88 in such a way that each inductor 102 isinductively coupled to a respective inductor 104. In the case wherefirst substrate 88 is made of semiconductor material, it will benecessary for the respective one or more inductors 104 to be integratedin the interface layer (here not shown and similar to the layer 34). Theinductors 102 are operatively coupled to respective output terminals ofcircuits (for example, they may comprise a transceiver/transponder, anAC-DC converter, a finite-state digital circuit, a microcontroller),here not illustrated, which comprise or are coupled to the first andsecond piezoresistive sensing elements 28, 29, for example connected viaa Wheatstone bridge or forming part of a ring oscillator circuit so asto receive the voltage signals generated as a result of the deformationof the membrane 19 and of the monolithic body 16, during use of thepressure sensor, and transfer said signals to the respective inductors104. The inductors 104 are coupled to conductive paths (not illustrated)to transfer the signal of detection of the pressure P outside thepressure sensor, for example to the control unit 4 of FIG. 1. Thepressure sensor may be supplied via further electrical contact pads (notillustrated) or via the inductors 102, 104 in a known way.

According to a further embodiment of a pressure sensor 105 (illustratedin FIG. 10), one or more inductors 106 are integrated in the interfacelayer 34. However, the first substrate 88 does not integrate respectiveinductors. Inductors 109 are instead provided in an external board, forexample a PCB (printed-circuit board) 110. During mechanical coupling ofthe pressure sensor 105 of FIG. 10 to the PCB 110, the pressure sensor105 is set on the PCB 110 in such a way that the inductors 106 areinductively coupled, in use, to the inductors 109. The inductors 106 and109 are appropriately sized in order to guarantee inductive coupling,and the substrate 88 extending between them should preferably have ahigh resistivity (for example, it may be intrinsic silicon or adielectric material such as a ceramic or glass) so as to prevent onsetof eddy currents. For instance, the inductors 109 are larger in sizethan the inductors 106.

Owing to the presence of the PCB 110, the pressure P is applied, in thisexample, on the second substrate 35.

Appropriate electrical connections are provided, in a per se knownmanner, on the PCB 110, for acquiring an electrical signal from theinductors 109 and sending it, for example, to the control unit 4 of FIG.1 to be processed. The pressure sensor may be supplied via furtherelectrical contact pads (not illustrated) or via the inductors 106, 109in a known way.

FIG. 11 shows, in top view, a further embodiment of a pressure sensor115 where the first substrate 32 has an extension, in the plane XY,smaller than the respective extension of the monolithic body 16. Inparticular, the first substrate 32 is here modeled in such a way as toexpose selective portions of the surface of the interface layer 34 thatextends over the monolithic body 16. The exposed selective portions arecorner regions of the interface layer 34 that extends over themonolithic body 16 (here assumed as being quadrangular, in particularsquare). Extending in the area corresponding to the exposed regions ofthe interface layer 34 is a plurality of contact pads 118 of conductivematerial, designed to be electrically contacted, for example by metalstrips 119 (e.g., copper strips). The contact pads 118 are in turn inelectrical contact with respective terminals of the circuits thatcomprise the first and second piezoresistive elements 28 and 29 foracquiring the signal transduced by them. Further electrical contact pads(not illustrated) may be provided for sending the power supply to thepressure sensor.

FIG. 12 shows a further embodiment of a pressure sensor 120. Thepressure sensor 120 of FIG. 12 is similar to the pressure sensor 50 ofFIG. 5. Elements of the pressure sensor 120 and of the pressure sensor50 that are in common are here not described or illustrated any furtherand are designated by the same reference numbers.

The pressure sensor 120 further comprises a first blade connector 122and a second blade connector 124 (also known as “fastons”); the firstblade connector 122 extends over the exposed side of the monolithic body56, whereas the second blade connector 124 extends over the exposed sideof the base substrate 52. In this way, the monolithic body 56 and thebase substrate 52 are sandwiched between the first and second bladeconnectors 122, 124.

The first and second blade connectors 122, 124, which are made ofconductive material, in particular metal, have the function of sendingthe power supply to the pressure sensor 120. For instance, the firstblade connector 122 is biased at a supply voltage V_(DD), whereas thesecond blade connector 124 is biased at a reference voltage, for examplethe ground voltage GND. For this purpose, in the coupling regionsbetween the monolithic body 56 and the first blade connector 122, and inthe coupling regions between the base substrate 52 and the second bladeconnector 124, there extend respective electrical contact pads (notillustrated). In order to connect the second blade connector 124electrically to the circuits (not illustrated, which comprise or areconnected to the piezoresistive sensing elements 68, 69) in themonolithic body 56, it is necessary for at least one portion (forexample, the outer ring) of the anchorage elements 54 to be conductive.Furthermore, the base substrate 52 and the monolithic body 56 mustpresent a low resistivity.

According to one embodiment of the present disclosure, the first andsecond blade connectors 122, 124 further have the function of sendingthe signals transduced by the piezoresistive sensing elements 68, 69outside the pressure sensor 120, for example to the control unit 4 ofFIG. 1. In this case, according to techniques in themselves known, theelectrical carrier signal (supply signal) is modulated in such a way asto function as data-carrying medium, for carrying also the signaltransduced by the piezoresistive elements 68, 69 (signal at output, forexample, from the respective Wheatstone-bridge circuits), or else saidsupply signal may be a constant voltage, superimposed then on which is adigital signal that carries the information of the physical quantitymeasured.

The pressure sensor described, according to the respective embodiments,presents numerous advantages.

In the first place, it presents a high full-scale value and enablesmeasurement of pressures with a double measuring scale, a first scalefor measuring low pressures, and a second scale for measuring highpressures. Both measurements are made with high precision. Inparticular, the pressure sensor described integrates within a samemonolithic body of semiconductor material the elements sensitive to highand low pressures, with contained costs and limited complexity ofproduction.

The pressure sensor makes a measurement of a differential type betweenone or more sensing elements and one or more piezoresistive referenceelements and is consequently insensitive to variations of environmentalparameters or to process spread.

Finally, it is clear that modifications and variations may be made towhat has been described and illustrated herein, without therebydeparting from the scope of the present disclosure.

In particular, it is clear how the shape of the monolithic body may bedifferent from what has been described and illustrated. In particular,the cross-section of the monolithic body may be circular or generallypolygonal, instead of being quadrangular or square as described. Alsothe first cavity 18 may have a shape different from what has beenillustrated, for example a circular or generically polygonalcross-section. Likewise, also the second cavity 38 may have a shapedifferent from what has been illustrated, for example a circular orgenerically polygonal cross-section.

Irrespective of the particular embodiment described, the piezoresistivesensor elements could be obtained using ion-implantation techniques,instead of by diffusion.

Irrespective of the particular embodiment described, it is possible touse electrical connections, between the piezoresistive elements,different from the Wheatstone bridge, for example a ring oscillatorcircuit, or some other connection still.

It is likewise possible to use a single piezoresistive sensing elementfor detecting deflections of the first membrane during the firstoperating condition, and a further single piezoresistive sensing elementfor detecting deflections of the second membrane (monolithic body)during the second operating condition of the pressure sensor.

Irrespective of the particular embodiment described, further, thepiezoresistive elements may be located in a position different from theone illustrated.

Irrespective of the particular embodiment described, it is furtherpossible to form, for example within the first substrate or the secondsubstrate, an electronic measuring circuit, so as to provide a pressuremeasuring device integrated in a single die.

In addition, the focusing regions and the anchorage regions could beobtained also using non-dielectric material, for example conductivematerial or semiconductor material.

Furthermore, using a semiconductor material different from silicon, forexample gallium arsenide, the sensing elements could have piezoelectriccharacteristics instead of piezoresistive ones.

Finally, it is pointed out that the pressure sensor 15 mayadvantageously be used also in other applications to measure highpressure values with a double measuring scale.

The various embodiments described above can be combined to providefurther embodiments. These and other changes can be made to theembodiments in light of the above-detailed description. In general, inthe following claims, the terms used should not be construed to limitthe claims to the specific embodiments disclosed in the specificationand the claims, but should be construed to include all possibleembodiments along with the full scope of equivalents to which suchclaims are entitled. Accordingly, the claims are not limited by thedisclosure.

The invention claimed is:
 1. A pressure sensor with double measuringscale, comprising: a flexible body configured to undergo, at least inpart, deflection as a function of a pressure acting in a direction; asubstrate arranged facing a first side of the flexible body; atransduction assembly configured to generate a first output signal and asecond output signal as a function of deflections of respective firstand second portions of the flexible body; a first focusing regionarranged between the substrate and the flexible body and configured toconcentrate, during a first operating condition, a first pressure valueof said pressure in the first portion of the flexible body and generatea deflection of the first portion of the flexible body; and a secondfocusing region fixed to the flexible body and configured to contact thefirst substrate, during a second operating condition, concentrate asecond pressure value of said pressure in the second portion of theflexible body, and generate a deflection of the second portion of theflexible body.
 2. The pressure sensor according to claim 1, furthercomprising a cavity between the substrate and the flexible body, whereinthe first focusing region extends in the cavity and has a firstthickness equal to a distance existing between the first substrate andthe flexible body, and the second focusing region extends in the cavityand has a second thickness smaller than said first thickness.
 3. Thepressure sensor according to claim 1, wherein the transduction assemblyis configured to generate the first output signal during the firstoperating condition by correlating the deflection of the first portionof the flexible body to the first pressure value, and to generate thesecond output signal during the second operating condition bycorrelating the deflection of the second portion of the flexible body tothe second pressure value.
 4. The pressure sensor according to claim 3,wherein: the transduction assembly includes a first piezoelectricelement arranged on the first portion of the flexible body and a secondpiezoelectric element arranged on the second portion of the flexiblebody; and the second focusing region is positioned between the first andsecond piezoelectric elements.
 5. The pressure sensor according to claim1, wherein the flexible body includes a buried first cavity directlyfacing the first portion of the flexible body in such a way that thefirst portion of the flexible body extends suspended on the buried firstcavity to form a membrane.
 6. The pressure sensor according to claim 5,further comprising a second cavity between the substrate and theflexible body, wherein the first focusing region extends in the secondcavity and has a first thickness equal to a distance existing betweenthe substrate and the flexible body, and the second focusing regionextends in the second cavity and has a second thickness smaller thansaid first thickness, wherein the thickness of the second focusingregion in said direction, and a dimension of the buried first cavity insaid direction, are chosen in such a way that the membrane comes intocontact with a bottom of the buried first cavity upon contact betweenthe second focusing region and the flexible body.
 7. The pressure sensoraccording to claim 6, wherein the dimension of the buried first cavityin the direction of action of the pressure is equal to a correspondingdimension of the second cavity at the second focusing region.
 8. Thepressure sensor according to claim 5, wherein said transduction assemblycomprises first piezoresistive elements arranged, at least in part, insaid membrane.
 9. The pressure sensor according to claim 5, wherein saidtransduction assembly further comprises second piezoresistive elementsarranged in the second portion of the flexible body, outside saidmembrane.
 10. The pressure sensor according to claim 9, wherein saidsecond portion of the flexible body that houses the secondpiezoresistive elements is a solid and compact region of the flexiblebody.
 11. The pressure sensor according to claim 9, wherein the firstpiezoresistive elements are electrically connected together in a firstWheatstone-bridge circuit, or a first ring oscillator circuit,configured to supply the first output signal; and the secondpiezoresistive elements are electrically connected together in a secondWheatstone-bridge circuit, or a second ring oscillator circuit,configured to supply the second output signal.
 12. The pressure sensoraccording to claim 5, wherein the membrane has a thickness in thedirection of action of the pressure between 1 μm and 60 μm.
 13. Thepressure sensor according to claim 1, wherein said first pressure valueis in a range 0-20 N and said second pressure value is higher than 20 N.14. The pressure sensor according to claim 1, wherein the flexible bodyincludes: a monolithic region having a thickness at the second portionalong the direction of action of the pressure, between 50 μm and 900 μm;and an interface layer, extending between the monolithic region and thefirst and second focusing regions, configured to distribute saidpressure uniformly over said monolithic region.
 15. A pressure measuringdevice, comprising: a measuring circuit; and a sensor assemblyelectrically coupled to the measuring circuit and including a pressuresensor with double measuring scale, the pressure sensor being configuredto receive a pressure acting in a direction and including: a flexiblebody configured to undergo, at least in part, deflection as a functionof said pressure; a substrate arranged facing a first side of theflexible body; a transduction assembly configured to generate a firstoutput signal and a second output signal as a function of deflections ofrespective first and second portions of the flexible body; a firstfocusing region arranged between the first substrate and the flexiblebody and configured to concentrate, during a first operating condition,a first pressure value of said pressure in the first portion of theflexible body and generate a deflection of the first portion of theflexible body; and a second focusing region fixed to the flexible bodyand configured to contact the first substrate, during a second operatingcondition, concentrate a second pressure value of said pressure in asecond portion of the flexible body, and generate a deflection of thesecond portion of the flexible body.
 16. The device according to claim15, wherein said measuring circuit is integrated in the flexible body ofthe pressure sensor.
 17. The device according to claim 15, wherein thetransduction assembly is configured to generate the first output signalduring the first operating condition by correlating the deflection ofthe first portion of the flexible body to the first pressure value, andto generate the second output signal during the second operatingcondition by correlating the deflection of the second portion of theflexible body to the second pressure value.
 18. A system, comprising: apressure actuator configured to produce a pressure acting in adirection; and a pressure measuring device that includes a measuringcircuit and a pressure sensor with double measuring scale, the pressuresensor being configured to receive the pressure acting in the directionand including: a flexible body configured to undergo, at least in part,deflection as a function of said pressure; a substrate arranged facing afirst side of the flexible body; a transduction assembly configured togenerate a first output signal and a second output signal as a functionof first and second pressures values imparted respectively to first andsecond portions of the flexible body; a first focusing region arrangedbetween the first substrate and the flexible body and configured toconcentrate, during a first operating condition, the first pressurevalue in the first portion of the flexible body; and a second focusingregion arranged between the first substrate and the flexible body andconfigured to concentrate, during a second operating condition, thesecond pressure value in the second portion of the flexible body. 19.The system according to claim 18, comprising: a brake, wherein themeasuring circuit is configured to generate a control signal and thepressure actuator includes an electromechanical actuator configured toexert a braking action on said brake in response to the control signalgenerated by the measuring circuit.
 20. A method, comprising: inresponse to receiving a first pressure value imparted in a firstdirection to a first side of a flexible body of a pressure sensor,generating, through a first focusing region extending between a secondof the flexible body and a substrate, a first deflection of a firstportion of the flexible body in a second direction, opposite to thefirst direction; in response to receiving a second pressure valueimparted in the first direction to the first side of the flexible body,generating, through a second focusing region contacting the substrateand flexible body, a second deflection of a second portion of theflexible body in the second direction; detecting the first pressurevalue as a function of the deflection of the first portion of theflexible body; and detecting the second pressure value as a function ofthe deflection of the second portion of the flexible body.
 21. Themethod according to claim 20, wherein: the pressure sensor furthercomprises a first cavity, between the substrate and the flexible body,the second focusing region extends in the first cavity and is spacedapart from one of the substrate and flexible body in a rest position,and the flexible body includes a buried second cavity that directlyfaces the first portion of the flexible body in such a way that thefirst portion of the flexible body extends suspended on the buriedsecond cavity to form a membrane; detecting the first pressure value ifthe first pressure value is less than a threshold pressure value thatbrings the first membrane into contact with a bottom of the buriedsecond cavity; and detecting the second pressure value includesdetecting the second pressure value if the second pressure value isgreater than the threshold pressure value.
 22. The method according toclaim 21, wherein: detecting the first pressure value includes detectingthe first pressure value using a first piezoelectric element arranged onthe first portion of the flexible body; and detecting the secondpressure value includes detecting the second pressure value using asecond piezoelectric element arranged on the second portion of theflexible body.